云南白马寨Cu-Ni硫化物矿微量和铂族元素地球化学和矿床成因意义

利用锍镍试金富集-等离子体质谱(ICP-MS)测定法较系统分析了云南白马寨主要Cu-Ni硫化物矿石和主要围岩的PGE、Au、Cu和Ni含量,发现PGE含量均较低,其中块状硫化物矿石的∑PGE为78.2×10-9～556×10-9,橄榄辉石岩为0.472×10-9～67.0 ×10-9,辉长岩为0.847×10-9,二辉岩为0.76×10-9～0.809 ×10-9.后期煌斑岩的PGE也很低(2.98×10-9～4.07×10-9).各类矿石和围岩中∑PGE与Au, Ni与Cu之间呈明显的正相关关系.各类矿石的PGE原始地幔标准化曲线和Pt/Pd和Cu/Pd值与其各主要围岩非常相似,说明该矿Cu-Ni硫化物矿石为岩浆成因,且与围岩有成因上的联系.矿石和围岩较高的Pt/Pd值(平均0.83)显示其主要形成于单独的硫化物饱和事件,矿石中较高的Ir (0.77×10-9～5.52×10-9, 平均2.35×10-9)和Pd/Ir值 (4.76～296,平均138)显示硫化物矿石可能受到后期强烈的热液蚀变.白马寨硫化物矿石较高的187Os/188Os 初始值(0.456± 0.026)显示地壳物质的加入是成矿的重要因素.计算显示该矿硫化物矿石中地壳来源Os超过30%.     

Petrology and PGE Abundances of High‐Cr and High‐Al Podiform Chromitites and Peridotites from the Bulqiza Ultramafic Massif,Eastern Mirdita Ophiolite,Albania

The Bulqiza ultramafic massif, which is part of the eastern Mirdita ophiolite of northern Albania, is world renowned for its high-Cr chromitite deposits. High-Cr chromitites hosted in the mantle section are the crystallized products of boninitic melts in a supra-subduction zone (SSZ). However, economically important high-Al chromitites are also present in massive dunite of the mantle-crust transition zone (MTZ). Chromian-spinel in the high-Al chromitites and dunites of the MTZ have much lower Cr# values (100Cr/(Cr+Al)) (47.7–55.1 and 46.5–51.7, respectively) than those in the high-Cr chromitites (78.2–80.4), harzburgites (72.6–77.9) and mantle dunites (79.4–84.3). The chemical differences in these two types of chromitites are reflected in the behaviors of their platinum-group elements (PGE). The high-Cr chromitites are rich in IPGE relative to PPGE with 0.10–0.45 PPGE/IPGE ratios, whereas the high-Al chromitites have relatively higher PPGE/IPGE ratios between 1.20 and 7.80. The calculated melts in equilibrium with the high-Cr chromitites are boninitic-like, and those associated with the high-Al chromitites are MORB-like but with hydrous, oxidized and TiO2-poor features. We propose that the coexistence of both types of chromitites in the Bulqiza ultramafic massif may indicates a change in magma composition from MORB-like to boninitic-like in a proto-forearc setting during subduction initiation.     

南秦岭山阳—柞水矿集区夏家店金矿床微量-铂族元素地球化学特征及其对矿床成因的指示

夏家店金矿床位于南秦岭造山带内,是一个受构造和地层控制的大型金矿床,矿石类型为角砾岩型、碎裂岩型和石英脉型3种类型,赋矿围岩主要为寒武系水沟口组的炭泥质板岩、炭硅质板岩、硅质岩及白云岩,次为泥盆系西岔河组的角砾岩。本文对夏家店金矿床中矿石（角砾状炭硅质板岩、碎裂硅化白云岩、碎裂炭泥质板岩和石英脉状矿化的硅质岩）和围岩（硅质岩、硅化白云岩和硅质板岩）的微量元素、铂族元素（PGE）质量分数进行测试,进而探讨成矿物质来源以及矿床成因。结果表明：不同类型的矿石与其各自的围岩具有高度的相似性,均富集Sr、Ga、Zr等元素;不同类型的矿石稀土总量均高于各类围岩,但是两者具有相似的稀土配分模式,轻稀土富集,重稀土亏损,均表现出负Eu异常（δEu值为0.51~0.63）;不同类型的矿石PGE总量（7.71×10^-9~38.30×10^-9,平均值23.00×10^-9）均明显大于各类围岩PGE总量（1.28×10^-9~2.44×10^-9,平均值1.86×10^-9）,相比上地壳,不同类型的矿石均明显富集Os、Ir、Pt和Pd,亏损Ru、Rh,而各类围岩均富集Os,亏损Pt、Ru、Rh、Pd,但两者的铂族元素配分曲线具有高度相似性,呈Ru亏损的V型,为地壳的（Os）-Pt-Pd型配分模式。以上特征表明不同类型的矿石和围岩具有明显的微量、稀土元素和PGE地球化学继承性,暗示夏家店下寒武统有可能是重要的矿源层之一。同时,所有矿石和围岩的Au/Ir值（分别为4 821~299 666）和406~8 050）及Pd/Ir值（分别为16.9~588.0和15.2~47.5）变化范围均较大,两者Au/Ir值远高于炭质球粒陨石和原始地幔值、Pd/Ir值远高于岩浆成因矿石值,且夏家店金矿床矿石和围岩的PGE配分曲线与典型热液成因矿床一致。这些特征显示夏家店金矿床具有明显的热液成因,是构造-热液流体成矿作用的产物。     

西藏努日铜钼钨矿床辉钼矿微量元素、稀土元素地球化学特征——对矿床成矿流体性质的约束

为厘清努日铜钼钨矿床的成矿时代,以矿床中的辉钼矿为研究对象,用ICP-MS分析方法,开展了稀土元素和微量元素地球化学研究。结果显示,辉钼矿具有典型的轻重稀土分馏、轻稀土元素(LREE)富集的右倾配分模式,辉钼矿稀土元素具有强烈的Ce负异常和Eu负异常,前者可能为成矿流体本身具有高温高氧逸度导致,后者可能是与矽卡岩矿化有密切关系的黑云母花岗闪长岩浆在分离结晶过程中大量的斜长石晶出引起的,同时岩体蚀变过程中对成矿流体体系亏损铕有一定贡献。辉钼矿中Pb、Ba、V、Ni、Sr、Rb含量相对较高,U、Th含量非常低,Hf/Sm、Th/La远小于1,Nb/La远大于1,表明成矿流体早期以富F的来自于深部幔源的岩浆热液为主,而Y/Ho、Zr/Hf、Nb/Ta变化范围存在不同幅度的差异。表明主成矿期成矿流体在该阶段不同程度的混入了部分外来流体而富Cl,但总体特征仍以早期成矿流体为主。     

The Design of Re‐usable Carius Tubes for the Determination of Rhenium,Osmium and Platinum‐Group Elements in Geological Samples

The traditional Carius tube technique is cumbersome and requires skilful work to seal the Carius tube, which can be used only once. We describe a modification to the technique that does not require the use of a high‐temperature welding torch to melt the Carius tube to seal it. The newly designed Carius tube consists of a main body with a 3 mm‐thick glass wall, a neck and head with walls 4 mm in thickness, and an efficient screw‐thread stopper. These new features allowed the tube to be used repeatedly. We demonstrate relatively low procedural blanks derived for Re and Os, and platinum‐group elements (PGEs), using the redesigned tube. A temperature of 220 °C could be reached for about 5 ml of HNO₃ for a 47 ml tube and for 32 ml of inverse aqua regia for a 200 ml tube. This digestion technique can be used for routine analysis of Re and PGEs in geological samples.     

Determination of Platinum‐Group Elements and Re‐Os Isotopes using ID‐ICP‐MS and N‐TIMS from a Single Digestion after Two‐Stage Column Separation

We report an improved procedure for the determination of the platinum‐group elements (PGE) and Re, and Os isotopes from a single sample aliquot by isotope dilution (ID) using inductively coupled plasma‐mass spectrometry (ICP‐MS) and negative thermal ionisation mass spectrometry (N‐TIMS), respectively. A two‐stage column method was used to purify PGE‐Re from their sample matrix and interfering elements (e.g., Mo, Zr and Hf) after Os had been separated by CCl₄ solvent extraction. The first column separation step used cation exchange resin (AG50W‐X8) to concentrate PGE‐Re and some potential interfering elements (e.g., Mo, Zr and Hf). In the second step, N‐benzoyl‐N‐phenylhydroxylamine (BPHA) extraction resin was used to separate PGE‐Re from the remaining interfering elements, which all remained strongly absorbed to the resin. The method was used to determine the PGE and rhenium, and Os isotope ratios in a range of geochemical reference materials (TDB‐1, WGB‐1, BHVO‐2 and UB‐N). The obtained results agree well with those previously published. This new method enables PGE‐Re abundances and Os isotopic ratios to be determined on the same sample digestion, and circumvents the problems created by sample heterogeneity when comparing PGE and Re‐Os isotope data.     

Geochronology, Geochemistry and Sr-Nd-Pb-Hf Isotopes of No. I Complex from the Shitoukengde Ni–Cu Sulfide Deposit in the Eastern Kunlun Orogen, Western China: Implications for the Magmatic Source, Geodynamic Setting and Genesis

The Shitoukengde Ni-Cu deposit, located in the Eastern Kunlun Orogen, comprises three mafic–ultramafic complexes, with the No. I complex hosting six Ni-Cu orebodies found recently. The deposit is hosted in the small ultramafic bodies intruding Proterozoic metamorphic rocks. Complexes at Shitoukengde contain all kinds of mafic-ultramafic rocks, and olivine websterite and pyroxene peridotite are the most important Ni-Cu-hosted rocks. Zircon U-Pb dating suggests that the Shitoukengde Ni-Cu deposit formed in late Silurian(426–422 Ma), and their zircons have εHf(t) values of-9.4 to 5.9 with the older T_(DM1) ages(0.80–1.42 Ga). Mafic-ultramafic rocks from the No. I complex show the similar rare earth and trace element patterns, which are enriched in light rare earth elements and large ion lithophile elements(e.g., K, Rb, Th) and depleted in heavy rare earth elements and high field strength elements(e.g., Ta, Nb, Zr, Ti). Sulfides from the deposit have the slightly higher δ~(34)S values of 1.9–4.3‰ than the mantle(0 ± 2‰). The major and trace element characteristics, and Sr-Nd-Pb and Hf, S isotopes indicate that their parental magmas originated from a metasomatised, asthenospheric mantle source which had previously been modified by subduction-related fluids, and experienced significant crustal contamination both in the magma chamber and during ascent triggering S oversaturation by addition of S and Si, that resulted in the deposition and enrichment of sulfides. Combined with the tectonic evolution, we suggest that the Shitoukengde Ni-Cu deposit formed in the post-collisional, extensional regime related to the subducted oceanic slab break-off after the Wanbaogou oceanic basalt plateau collaged northward to the Qaidam Block in late Silurian.     

Mineralogy and Geochemistry of the High‐Cr Podiform Chromitite from the Cuobuzha Ophiolite,Yarlung Zangbo Suture Zone,Western Tibet,China: Implication for its Origin

The Cuobuzha high-Cr chromitites in the western segment of Yarlung Zangbo Suture Zone of Tibet are mainly hosted in the harzburgites as massive type, which are characterized by high concentrations of platinum group elements(PGE) ranging from 380 to 577 ppb, and low Pd/Ir ratios(<0.1). In mid-ocean ridge basalts(MORB)-normalized spidergrams, chromites of the Cuobuzha chromitites are depleted in Al, Ga, V, Mg and Zn, and enriched in Mn and Cr, sharing similar patterns with those of ophiolitic b...     

Petrogenesis of Ore‐Related Granodiorite Porphyry in the Jiande Copper Deposit,SE China: Implications for the Tectonic Setting and Mineralization

Adakitic rocks and related Cu–Au mineralization are widespread along eastern Jiangnan Orogen in South China. Previous studies have mainly concentrated on those in the Dexing area in northeastern Jiangxi Province, but information is lacking on the genesis and setting of those in northwestern Zhejiang Province. The Jiande copper deposit is located in the suture zone between the Yangtze and Cathaysia blocks of South China. This paper presents systematic LA–ICP–MS zircon U–Pb dating and element and Sr–Nd–Hf isotopic data of the Jiande granodiorite porphyry. Zircon dating showed that the Jiande granodiorite porphyry was produced during the Middle Jurassic (ca. 161 Ma). The Jiande granodiorite porphyry is characterized by adakitic geochemical affinities with high Sr/Y and La_N/Yb_N ratios but low Y and Yb contents. The absence of a negative Eu anomaly, extreme depletion in Y and Yb, relatively low MgO contents, and relatively high ²⁰⁷Pb/²⁰⁴Pb ratios, indicated that the Jiande granodiorite porphyry was likely derived from partial melting of the thickened lower continental crust. In addition, the Jiande granodiorite porphyry shows arc magma geochemical features (e.g., Nb, Ta and Ti depletion), with bulk Earth‐like ε_Nd (t) values (?2.89 to ?1.92), ε_Hf (t) values (?0.6 to +2.8), and initial ⁸⁷Sr/⁸⁶Sr (0.7078 to 0.7105). However, a non‐arc setting in the Middle Jurassic is indicated by the absence of arc rocks and the presence of rifting‐related igneous rock associations in the interior of South China. Combined with the regional Neoproterozoic Jiangnan Orogeny, it indicates that these arc magma geochemical features are possibly inherited from the Neoproterozoic juvenile continental crust formed by the ancient oceanic crust subduction along the Jiangnan Orogen. The geodynamic environment that is responsible for the development of the Middle Jurassic Jiande granodiorite porphyry is likely a localized intra‐continental extensional environment along the NE‐trending Jiangshan‐Shaoxing Deep Fault as a tectonic response to far‐field stress at the margins of the rigid South China Plate during the early stage of the paleo‐Pacific plate subduction. In terms of Cu mineralization, we suggest that the metal Cu was released from the subducted oceanic slab and reserved in the juvenile crust during Neoproterozoic subduction along the eastern Jiangnan Orogen region. Partial melting of the Cu rich Neoproterozoic juvenile crust during the Middle Jurassic time in the Jiande area caused the formation of adakitic rocks and the Cu deposit.     

Ore Genesis for Stratiform Ore Bodies of the Dongfengnanshan Copper Polymetallic Deposit in the Yanbian Area, NE China：Constraints from LA-ICP-MS in situ Trace Elements and Sulfide S–Pb Isotopes

The Dongfengnanshan Cu polymetallic deposit is one representative deposit of the Tianbaoshan ore district in the Yanbian area, northeast(NE) China. There occur two types of ore bodies in this deposit, the stratiform ore bodies and veintype ones, controlled by the Early Permian strata and the Late Hercynian diorite intrusion, respectively. Due to the ambiguous genetic type of the stratiform ore bodies, there has been controversy on the relationship between them and veintype ore bodies. To determine the genetic type of stratiform ore bodies, laser ablation inductively coupled plasma mass spectrometry(LA-ICP-MS) in situ trace elements and S–Pb isotope analysis have been carried on the sulfides in the stratiform ore bodies. Compared with that in skarn, Mississippi Valley-type(MVT), and epithermal deposits, sphalerite samples in the stratiform ore bodies of the Dongfengnanshan deposit are significantly enriched in Fe, Mn, and In, while depleted in Ga, Ge, and Cd, which is similar to the sphalerite in volcanic-associated massive sulfide(VMS) deposits. Co/Ni ratio of pyrrhotites in the stratiform ore bodies is similar to that in VMS-type deposits. The concentrations of Zn and Cd of chalcopyrites are similar to those of recrystallized VMS-type deposits. These characteristics also reflect the intermediate ore-forming temperature of the stratiform ore bodies in this deposit. Sulfur isotope compositions of sulfides are similar to those of VMS-type deposits, reflecting that sulfur originated from the Permian Miaoling Formation. Lead isotope compositions indicate mixed-source for lead. Moreover, the comparison of the Dongfengnanshan stratiform ore bodies with some VMStype deposits in China and abroad, on the trace elements and S–Pb isotope characteristics of the sulfides reveals that the stratiform ore bodies of the Dongfengnanshan deposit belong to the VMS-type, and have closely genetic relationship with the early Permian marine volcanic sedimentary rocks.     

U–Pb geochronology and Raman spectroscopy of zircons from the granites in the Xihuashan and Tieshanlong Deposit: Implications for W‐Sn mineralization in Southern Jiangxi Province,South China

The Xihuashan and Tieshanlong tungsten deposit is an important large quartz vein‐type W‐polymetallic deposit in the southern Jiangxi Province, eastern Nanling Range. Zircon U–Pb analyses of representative ore‐forming granites from the Xihuashan and Tieshanlong tungsten deposit yield ages of 146.3 ± 2.9 Ma and 146.0 ± 3.8 Ma, respectively. According to the zircon Raman spectroscopy, these granitic rocks are disturbed by different degrees of hydrothermal alteration, whereas most zircons exhibit primary oscillatory zoning and Th/U ratios in the range of magmatic zircon, which means the analysis results represent the crystallization age of metallogenetic granitic assemblages. In combination with regional geological data, it is suggested that the Late Jurassic is probably another important episode of granitic magmatism and W‐Sn mineralization in southern Jiangxi Provinces, even South China.     

Petrology,Geochemistry, and Fluid Inclusion Microthermometry of Sphalerite from the Laloki and Federal Flag Strata‐Bound Massive Sulfide Deposits,Papua New Guinea: Implications for Gold Mineralization

The Laloki and Federal Flag deposits are two of the many (over 45) polymetallic massive sulfide deposits that occur in the Astrolabe Mineral Field, Papua New Guinea. New data of the mineralogical compositions, mineral textures, and fluid inclusion studies on sphalerite from Laloki and Federal Flag deposits were investigated to clarify physiochemical conditions of the mineralization at both deposits. The two deposits are located about 2 km apart and they are stratigraphically hosted by siliceous to carbonaceous claystone and rare gray chert of Paleocene–Eocene age. Massive sulfide ore and host rock samples were collected from each deposit for mineralogical, geochemical, and fluid inclusion studies. Mineralization at the Laloki deposit consists of early‐stage massive sulfide mineralization (sphalerite‐barite, chalcopyrite, and pyrite–marcasite) and late‐stage brecciation and remobilization of early‐stage massive sulfides that was accompanied by late‐stage sphalerite mineralization. Occurrence of native gold blebs in early‐stage massive pyrite–marcasite‐chalcopyrite ore with the association of pyrrhotite‐hematite and abundant planktonic foraminifera remnants was due to reduction of hydrothermal fluids by the reaction with organic‐rich sediments and seawater mixing. Precipitation of fine‐grained gold blebs in late‐stage Fe‐rich sphalerite resulted from low temperature and higher salinity ore fluids in sulfur reducing conditions. In contrast, the massive sulfide ores from the Federal Flag deposit contain Fe‐rich sphalerite and subordinate sulfarsenides. Native gold blebs occur as inclusions in Fe‐rich sphalerite, along sphalerite grain boundaries, and in the siliceous‐hematitic matrix. Such occurrences of native gold suggest that gold was initially precipitated from high‐temperature, moderate to highly reduced, low‐sulfur ore fluids. Concentrations of Au and Ag from both Laloki and Federal Flag deposits were within the range (<10 ppm Au and <100 ppm Ag) of massive sulfides at a mid‐ocean ridge setting rather than typical arc‐type massive sulfides. The complex relationship between FeS contents in sphalerite and gold grades of both deposits is probably due to the initial deposition of gold on the seafloor that may have been controlled by factors such as Au complexes, pH, and fO₂ in combination with temperature and sulfur fugacity.